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Query: UMLS:C0038454 (stroke)
 147,016 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We investigated whether chronic deficiency of nitric oxide (NO) in stroke-prone spontaneously hypertensive rats (SHRSP) precipitates stroke and whether exogenous nitrates and other pharmacological agents can prevent stroke. Groups of five-week-old male SHRSP rats chronically received saline, L-nitro-arginine methyl ester (L-NAME) in saline, L-NAME along with pharmacological agents (L-arginine, isosorbide dinitrate, enalapril maleate and L-158,809; angiotensin receptor antagonist; 5,7-dimethyl-2-ethyl-3(-)[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]meth yl]-imidazo[4,5-b]pyridine) in saline to drink. The development of visible neurological deficits following various treatments was considered as an occurrence of stroke. Within hours following onset of stroke, the rats were anesthetized, catheterized and attached to a Cardiomax blood pressure recorder. SHRSP treated with L-NAME (10+/-2 mg/day) developed stroke in 11+/-2 days while no neurological deficit was seen in animals receiving saline till the end of the study period (35 days). Blockade of the renin-angiotensin system with enalapril or L-158,809 significantly delayed the onset of stroke (19+/-2 and 20+/-2 days, respectively), but caused only slight reductions in mean arterial blood pressure. These results suggest that chronic inhibition of NO synthase in SHRSP is associated with the development of stroke and such stroke appears to be renin-angiotensin system-dependent.
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PMID:Angiotensin receptor antagonists delay nitric oxide-deficient stroke in stroke-prone rats. 931 59

Two problems in the treatment of hypertension continue to be largely unsolved. The first, and more simple, is our inability to adequately control blood pressure in the majority of hypertensive patients. This not only reflects the difficulty of retaining patients in effective treatment programs, but also of convincing physicians to strive for optimal blood pressure levels. There is a continuing need for new antihypertensive drugs and combinations to help accomplish these goals. The second major problem is that the major clinical endpoints, including coronary events and renal failure, have not been adequately reduced by traditional therapies. Standard regimens, particularly those including diuretics, have protected against strokes and heart failure. Our improved understanding of vascular biology in hypertension has directed interest to the mechanisms in hypertensive patients that might accelerate atherosclerosis and vascular events in these individuals. This involves addressing the concomitant metabolic risk factors that comprise the "Hypertension Syndrome," and, perhaps of equal importance, finding therapies that directly inhibit unwanted types of growth and proliferative activities within the walls of critical arteries. Many substances within the endothelium and the vascular wall may participate as initiators or mediators of pathology, but most information thus far has focused on the renin-angiotensin system. Angiotensin converting enzyme inhibitors (and potentially angiotensin receptor blockers) have provided coronary and renal protection in various cardiovascular conditions, though not yet in formal hypertension trials. Calcium channel blockers have also shown promise, including recent stroke and cardiovascular benefits in patients with isolated systolic hypertension, but, again, definitive coronary data in hypertension are awaited. Unless concomitant conditions mandate the selection of a particular antihypertensive drug class, physicians currently have a dilemma: should they choose drugs from older classes that have not provided full protection? Or, should they prescribe newer agents with exciting potential but with, as yet, unproved endpoint benefits in hypertension? Until currently ongoing prospective trials of antihypertensive therapy are completed, physicians must be guided by their own interpretations of the available data.
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PMID:Translating data on antihypertensive drugs into clinical practice. 965 68

These experiments examined the effectiveness of chronic blockade of the renin angiotensin system with either valsartan or benazeprilat on survival, blood pressure and end-organ damage in salt-loaded stroke-prone SHR. Valsartan or benazeprilat given continuously by subcutaneous osmotic minipump beginning at 10.5 weeks of age lowered blood pressure, as determined by radiotelemetry, prevented proteinuria, prolonged survival and decreased the severity of histopathological changes in the heart and kidney. These results indicate that angiotensin receptor blockade affords a similar degree of protection as inhibition of angiotensin converting enzyme in salt-loaded stroke-prone SHR. Furthermore, our results are consistent with a primary contribution of angiotensin II to the maintenance of blood pressure and support a principal role for angiotensin II-dependent mechanisms in the development of end-organ damage in the salt-loaded stroke-prone SHR.
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PMID:Protective effects of valsartan and benazeprilat in salt-loaded stroke-prone spontaneously hypertensive rats. 976 21

Two major problems continue to challenge hypertension experts and clinical practitioners. The first is the apparently simple issue of controlling blood pressure; only one-quarter of hypertensive patients in the United States have blood pressures reduced to less than 140/90 mm Hg. Even those known to be receiving treatment have barely a 50% success rate. Explanations include inadequate commitments by physicians to achieve target blood pressures, but it is also likely that effectively decreasing blood pressure--despite the currently available panoply of antihypertensive agents--is a truly difficult task. The second problem is that despite our success in decreasing stroke incidence, hypertension treatment with traditional agents, largely diuretic-based, has not adequately protected patients against coronary events and renal insufficiency. Such new drug classes as angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers, and calcium channel blockers exhibit vascular effects that might inhibit atherosclerotic changes and reduce clinical events, but we are still awaiting definitive confirmation of these properties from ongoing clinical outcomes studies in hypertension. Therapy with fixed combinations of antihypertensive drugs is now recognized as a potentially useful approach. Innovative combinations, including ACE inhibitors and calcium channel blockers, can provide enhanced antihypertensive efficacy while avoiding or minimizing adverse metabolic and clinical side effects. These approaches are also convenient and cost-effective. It remains to be learned whether newer drug combinations might exhibit additive cardiovascular protective actions.
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PMID:Unsolved problems in treating hypertension: rationale for new approaches. 979 48

The vascular structural remodeling function may be altered in genetically hypertensive animals, spontaneously hypertensive rats (SHR). To examine this possibility, we measured the activity of mitogen-activated protein (MAP) kinases, enzymes believed to be involved in the pathway for cell proliferation, in rat aorta strips, and examined whether the endothelium removal-induced MAP kinase activation function is altered in SHR and whether vascular angiotensin and endothelin systems are responsible for the alteration of MAP kinase activation in SHR. Male 4-week-old SHR and age-matched Wistar Kyoto rats (WKY) supplied by Charles River Japan were used. Endothelium-denuded aorta strips were incubated at 37 degrees C in medium. MAP kinase activity after incubation was time-dependently increased in strips from SHR and WKY. MAP kinase activation was greater in SHR than in WKY aorta strips. Similarly, MAP kinase activation was enhanced in aorta strips from 4-week-old SHR and stroke prone SHR supplied by the Diseases Model Cooperative Research Association (Kyoto, Japan). In aorta strips from SHR and WKY, the angiotensin receptor antagonist, losartan, and the endothelin receptor antagonist, cyclo (D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl)(BQ123), caused concentration-dependent inhibition of MAP kinase activation. The losartan-induced but not BQ123-induced inhibition of MAP kinase activation was greater in SHR than in WKY aorta strips. Angiotensin II caused a concentration-dependent increase in MAP kinase activity and the angiotensin II-induced MAP kinase activation was greater in SHR than in WKY aorta strips. These results indicate that endothelium removal-induced MAP kinase activation is enhanced in aorta strips from young SHR, suggesting that vascular structural remodeling function may be enhanced in SHR. It appears that the enhancement of MAP kinase activation results, at least in part, from enhanced function of vascular angiotensin system in SHR.
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PMID:Vascular mitogen-activated protein kinase activity is enhanced via angiotensin system in spontaneously hypertensive rats. 1039 23

Left ventricular hypertrophy (LVH), a target-organ response to chronic pressure or volume overload, is associated with its own independent risks of death in patients with hypertension. Numerous studies have shown that LVH increases the risk of coronary heart disease, congestive heart failure, stroke or transient ischemic attack, all-cause deaths, and sudden death. Although the mechanisms by which LVH develops are incompletely understood, the renin-angiotensin system may play an important role. All major classes of antihypertensive agents (calcium channel blockers, diuretics, beta-blockers, angiotensin-converting enzyme inhibitors) can cause LVH regression but not all to the same degree. Angiotensin-converting enzyme inhibitors may provide the most pronounced reduction in left ventricular mass per millimeter of mercury of blood pressure reduction. In addition, animal studies and human trials show promise for the regression of LVH with the use of angiotensin receptor blockers (ARBs). Because ARBs act specifically on the AT(1) receptor, angiotensin II can exert its favorable effects on cell growth inhibition through the AT(2) receptor. One small study that compared the ARB valsartan with atenolol found significant regression of LVH with the ARB by 8 months of treatment.
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PMID:Therapeutic options in minimizing left ventricular hypertrophy. 1061 82

Hypertension is often referred to as the "silent killer" because most hypertensive patients are asymptomatic until cardiovascular sequelae such as stroke, myocardial infarction, heart failure, or renal failure occur. LVH is a common finding in patients with hypertension, especially African-Americans. Data from the Framingham Heart Study indicate that LVH is an independent risk factor for major cardiovascular events. In the Amlodipine Cardiovascular Community Trial, 37% of 124 hypertensive patients screened by means of echocardiography had LVH at baseline. Although there was no difference in the prevalence of LVH by gender or age, African-American patients were nearly twice as likely to have LVH than white patients (64% vs. 34%, p<0.05). Hence, aggressive therapy to reach target goals outlined in the Sixth Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC VI) is especially important in this group of patients. Even lifestyle modifications such as weight reduction and limitation of salt intake, if sufficiently aggressive, can lead to regression of LVH, as demonstrated by results of the Treatment of Mild Hypertension Study (TOMHS). Most classes of antihypertensive drugs are effective in causing regression of LVH. Vasodilators, such as minoxidil and hydralazine, do not have an effect on regression, possibly because reflex tachycardia and stimulation of catecholamines and the renin-angiotensin system associated with these agents may negate the benefit of reduced afterload. There is some controversy regarding the ability of the angiotensin receptor blockers to reduce LVH. In some studies, these agents were associated with regression, whereas in others they were not. Whether targeting LVH as the primary treatment goal in hypertensive patients will have long-term benefits on outcome above and beyond simply reducing blood pressure is not clear.
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PMID:Case 3: A patient with systemic hypertension and left ventricular hypertrophy. 1072 68

Hypertension is prevalent world-wide, and it affects over 50 million individuals in the United States alone. African Americans (blacks) have a high prevalence of hypertension, develop it at an earlier age, and suffer excessively from severe or malignant hypertension. They also have a high prevalence of target organ damage attributable to hypertension, including left ventricular hypertrophy, stroke, end-stage renal disease (ESRD) and coronary artery disease. Hypertensive nephrosclerosis is particularly more prevalent in blacks compared to whites, and there is evidence that factors in addition to elevated blood pressure contribute to its pathogenesis. Transforming growth factor-beta 1 (TGF-beta1) is a fibrogenic cytokine that has been implicated in the development and progression of experimental and human renal diseases. We have demonstrated that blacks with ESRD have higher circulating levels of TGF-beta1 protein compared to whites with ESRD. We have also found that hyperexpression of TGF-beta1 is more frequent in blacks with hypertension than in whites. We propose that TGF-beta1 hyperexpression may be an important mediator of hypertension and hypertensive nephrosclerosis. We hypothesize also that the increased frequency of TGF-beta1 hyperexpression may contribute to the excess burden of ESRD in blacks. Based on our hypotheses, and the observations that angiotensin-converting enzyme inhibitors and angiotensin receptor antagonists reduce angiotensin II-mediated stimulation of TGF-beta1 production, we propose that treatment with these agents might be efficacious in preventing or slowing the progression of target organ damage in hypertensive blacks.
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PMID:Hypertension-induced organ damage in African Americans: transforming growth factor-beta(1) excess as a mechanism for increased prevalence. 1098 Nov 47

Hypertensive nephrosclerosis is a leading cause of end-stage renal disease; therefore, strategies to prevent the development of renal disease require close study. Here it is demonstrated that transient treatment of prepubescent rats with angiotensin inhibitors attenuated their susceptibility to the development of hypertensive nephrosclerosis after maturation. Stroke-prone spontaneously hypertensive Izumo strain rats were divided into four groups, treated with vehicle, the angiotensin-converting enzyme inhibitor (ACEI) delapril (40 mg/kg per d), the angiotensin receptor antagonist (AT1R-Ant) candesartan cilexetil (1 mg/kg per d), or the vasodilator hydralazine (25 mg/kg per d) from weaning to puberty (3 to 10 wk of age), and then monitored without treatment for 6 mo. BP in the ACEI- and AT1R-Ant-treated groups remained significantly decreased, compared with the untreated and hydralazine-treated groups. Moreover, marked proteinuria and nephrosclerosis developed in the untreated and hydralazine-treated groups at 30 wk but were suppressed in the ACEI- and AT1R-Ant-treated groups. Of interest, plasma renin activity, plasma angiotensin II concentrations, and renal renin mRNA levels were reduced by >50% in the ACEI- and AT1R-Ant-treated rats, suggesting that the treatments may have attenuated the development of nephrosclerosis by overcoming the susceptibility of stroke-prone spontaneously hypertensive rats to overactivation of the renin-angiotensin system.
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PMID:Temporary treatment of prepubescent rats with angiotensin inhibitors suppresses the development of hypertensive nephrosclerosis. 1127 26

Platelets are formed from, and their function determined by, bone marrow megakaryocytes (MK). Previous studies have found that hypertension is associated with accentuated platelet function and that some antihypertensive drug classes have antiplatelet activity. We measured MK ploidy (DNA content), size, granularity, and expression of the adhesion molecule glycoprotein (GP) IIIa, using flow cytometry and measures of platelet function, in 12 untreated hypertensive patients and 14 normotensive subjects. Eight hypertensive patients were then treated with losartan (50 mg daily), an angiotensin receptor antagonist that lowers blood pressure, and MK and platelet parameters re-measured after 6 weeks. Hypertensive patients had, as compared with matched normotensive subjects: increased MK ploidy (mean +/- SD) 22.9 +/- 2.2 N versus 20.8 +/- 1.6 N (2P = 0.009); increased platelet size, 10.67 +/- 1.03fl versus 9.26 +/- 0.72fl (2P < 0.001); increased platelet expression of GP IIIa, 108.6 +/- 22.5 versus 92.0 +/- 12.3 (2P = 0.036); and reduced platelet count, (207 +/- 52) x 10(9)/l versus (257 +/- 55) x 10(9)/l (2P = 0.026). Losartan significantly reduced MK ploidy, 22.6 +/- 2.2 N versus 21.4 +/- 1.9 N (2P = 0.006); MK size, 607 +/- 22 versus 579 +/- 16 (2P = 0.003); and lengthened cutaneous bleeding time, 424 +/- 86s versus 563 +/- 164s (2P = 0.011), in hypertensive patients. Losartan did not alter MK granularity or GP IIIa expression, or platelet count, size, mass, GP IIIa expression, or aggregation. The data suggest that platelet changes in hypertension may be secondary to changes in MKs, and that anti-hypertensive treatment can alter MKs and the function of platelets they produce. Since antihypertensive therapy reduces the risk of stroke and myocardial infarction, MKs are a novel therapeutic target for the prevention of vascular events.
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PMID:Prothrombotic megakaryocyte and platelet changes in hypertension are reversed following treatment: a pilot study. 1130 15


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